Internal combustion engines, such as those used in automotive vehicles, conventionally include a fuel system which provides fuel to the engine at a rate that varies with one or more operating conditions such as the rate of air flow to the engine or a combination of engine speed and load. At each engine operating point, during operation at normal temperatures, the fuel flow is carefully controlled to produce the desired engine torque.
During operation at less than normal temperatures, however, that same fuel flow is insufficient to produce the torque desired for the particular engine operating point. Accordingly, such engines also conventionally include a choke or other cold enrichment mechanism to increase fuel flow and thus enrich the air-fuel mixture during low temperature operation. A sufficiently enriched air-fuel mixture would assure that the engine would produce adequate torque during the warm-up period before it reaches normal operating temperature.
It has been recognized, however, that an enriched air-fuel mixture increases fuel consumption and contributes to emissions of hydrocarbons and carbon monoxide in the engine exhaust gases. To minimize those effects, the prior cold enrichment mechanisms schedule the amount of enrichment with time, engine temperature, and other engine operating conditions. Yet any such schedule is only an approximation of the cold enrichment actually required: When the cold enrichment schedule falls short of the required amount, the engine will produce insufficient torque; when the cold enrichment schedule exceeds the required amount, the engine will consume unnecessary fuel and create unnecessary exhaust emissions.